As disclosed in U.S. Pat. No. 4,594,453 (Ranken et al.-I), it is known that various (hydrocarbylthio)aromatic amines are useful as intermediates in the preparation of biologically-active materials, polyurethanes, etc.; and they can be prepared by reacting an aromatic amine with a hydrocarbyl disulfide in the presence of a catalytic amount of a Lewis acid. The preferred catalysts of Ranken et al.-I are metal halides, such as aluminum chloride, boron trifluoride, boron trichloride, ferric chloride, and zinc chloride.
In the case of at least some aromatic amines, it has been found that the preferred catalysts identified by Ranken et al.-I have the disadvantages of effecting the desired hydrocarbylthiations at too slow a rate to be completely satisfactory and of sometimes providing too low a yield of product. These disadvantages can frequently be overcome by the use of the hydrogen iodide, ammonium iodide, and cuprous iodide catalysts of U.S. Pat. No. 4,670,597 (Ranken et al.-II), the metal iodide and bromide catalysts of U.S. Pat. No. 4,670,598 (Davis-I), or the iodine-promoted metal and metal halide catalysts of U.S. Pat. No. 4,751,330 (Davis-II). However, there is still a need for improvement in the reaction rates and/or yields of mono(hydrocarbylthio)-aromatic amines in the hydrocarbylthiation processes, and it would also be desirable to use a catalyst which could be recycled.